1. Field of the Invention
The present invention relates to an incandescent light bulb, and more particularly to an incandescent light bulb having more than one light emitting filament wherein a second and any subsequent filament is activated for operative use only when a preceding filament burns out.
2. Description of the Prior Art
Incandescent light bulbs are well known in the prior art. In view of the great practical and economic siginficance of the incandescent light bulb a multitude of patent and other disclosures have described various designs of construction and modifications of the incandescent light bulb.
It is a well known fact that an incandescent light bulb has a limited life time, and after a certain number of hours of operation its more essential structural component, the light emitting filament burns out rendering the light bulb inoperative. It is readily understood that a prolonged useful life of an incandescent light bulb is desireble from an economic standpoint. Furthermore incandescent light bulbs are used in many situations where failure of the light bulb creates a safety hazare, for example failure of a light bulb in an automobile stop or tail-light or in an automobile headlight creates a traffic hazard of which the operator of the automobile may not even be aware. In many other situations as well, abrupt, inadvertent malfunction of an incandescent light bulb caused by a burnt-out filament creates a hazard and nuisance in that immediate replacement of the malfunctioning light bulb is either impossible or very inconvenient.
In an effort to prolong the useful life of the incandescent light bulb, the prior art has made many attempts and advances. For example a recent disclosure describing an incandescent lamp having increased life can be found in Winter U.S. Pat. No. 3,942,063. However the light bulb disclosed in the Winter patent as well as other light bulbs of the prior art merely provide a prolonged life of the filaments and do not incorporate a self-replacing feature.
It should be readily apparent from the above that the prior art has been constantly striving to design an incandescent light bulb having a truly extended life. All that effort and time spent in developing a prolonged life light bulb has not, until the present invention, resulted in a light bulb having a self-replacing feature incorporated in the light bulb of the present invention.